Kept in a loft for many years, the battery leaked and damaged the motherboard:

With any other computer I would have just tried to find a replacement, but I had to try and fix this one as it was the one I actually used back in the day. So, I cleaned up the area and had to find where the damaged traces linked to so I could re-wire them, which included desoldering some parts so I could see the board.

The initial clean-up, removal of the old battery and a few components to clean up the surrounding area:

I later removed a few more things. Partly just to do more cleaning and also because I had to try changing a few parts, like the U31 chip. It also helped to follow the traces.

I also de-soldered the big keyboard chip on the left there and fitted it in a new socket.

The rest was using the multimeter to find where those traces started and ended. You can see in the first picture how messed up they are.